VALICALC · ENGINEERING WORKFLOW

Gear drive ratio and pitch geometry check

Connect tooth-count ratio to output RPM, then verify compatible module/diametral pitch and nominal pitch diameters for a simple gear pair.

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What do I need to know first?

Driver/driven tooth counts and input speed
Module or diametral pitch and compatible gear conventions
Whether the gears are standard external spur gears

Goal and model boundaries

Check ratio and nominal geometry for a simple spur-gear pair without implying tooth-strength or life approval.

The linked standard geometry tools do not validate profile shift, tooth strength, backlash or lubrication.
Compound trains require the product of stage ratios, with separate direction checks.

Establish the ratio
Enter driver and driven tooth counts.
Reduction ratio = driven teeth / driver teeth.
Expected output
The ideal single-stage reduction ratio.
Next step
Apply it to the driver RPM in Gear RPM.
CalculatorGear Ratio Calculator →Calculate reduction ratio
Check output speed
Use the same tooth counts and input RPM.
Output RPM = input RPM × driver teeth / driven teeth.
Expected output
Ideal output rotational speed.
Next step
Check module/DP compatibility and nominal dimensions.
CalculatorGear RPM Calculator →Calculate driven RPM
Confirm pitch geometry
Select module/DP and tooth count; distinguish pitch from outside diameter.
Pitch diameter = module × teeth; DP = 25.4/module for the same nominal pitch.
Expected output
Nominal pitch diameter and pair centre-distance basis.
Next step
Verify actual manufacturer drawings and strength/contact design separately.
ReferenceGear Module Chart →Compare module scenarios ReferenceModule ↔ Diametral Pitch Chart →Convert pitch conventions CalculatorGear Center Distance Calculator →Check nominal centre distance

Units and context

Module uses mm per tooth; DP uses teeth per inch of pitch diameter.
The same ratio can be reported as reduction or speed multiplier; identify the driver explicitly.

Common mistakes to avoid

Swapping driver and driven tooth counts
Mating gears with incompatible pitch or pressure angle
Treating outside diameter as pitch diameter

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